Strike-slip tectonics within the SW Baltic Sea and its relationship to ...

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orientation of inherited fault zones to the extensional
and compressional stress fields. Regional obliquity of
inherited basement faults and the stress field often
results in formation of transverse fault zones during
rifting and subsequent basin development (Cartwright,
1987), as well as strike-slip movements and development
of positive flower structures during inversion
(Harding, 1985; Woodcock and Schubert, 1994;
Lihou and Allen, 1996). Within hinge zones of
inversion-related folds, thickness reductions of syninversion
deposits accompanied by localised progradational
pattern are often observed and indicate syndepositional
tectonic activity (Cartwright, 1989).
High-resolution seismics is a very powerful research
tool in studies of the Cenozoic evolution of
the offshore areas, as is shown, e.g. by recent studies
of Cenozoic history of the Danish North Sea. In this
area, shallow seismic profiles imaged both detailed
depositional architecture of Cenozoic deposits
(Michelsen et al., 1998; Clausen et al., 1999), often
deformed by tectonic (e.g. glacitectonic) and erosional
processes (Huuse and Lykke-Andersen,
2000a,b), as well as their immediate substratum
(Huuse, 1999). Regional coverage of shallow seismic
data combined with well information and petroleum
seismic data provided a database allowing for construction
of a regional model of Cenozoic evolution
of this large offshore area (Clausen and Huuse, 1999;
Huuse et al., 2001).
New offshore high-resolution seismic data from the
southern Baltic Sea are presented here. This data set
documents modes of the Late Cretaceous inversion
tectonics within the wide zone stretching between the
island of Borholm and the Polish coast, in particular
large amount of strike-slip deformations related to the
inversion. The interpretation has led to an updated and
refined tectonic map of the SW Baltic Sea.
2. Geological setting
The SW Baltic Sea forms part of a very complicated
area where several important regional tectonic zones
and lines overlap and merge, including Sorgenfrei–
Tornquist Zone (STZ), Teisseyre–Tornquist Zone
(TTZ) and the Caledonian deformation front (Fig. 1;
Pharaoh, 1999 and references therein). Research projects
including deep seismic reflection profiling have
P. Krzywiec et al. / Tectonophysics 373 (2003) 93–105
Fig. 1. Location of the study area (rectangle) and its relationship to
the major crustal features of the North Europe, including the
Precambrian East European Platform, the Palaeozoic West European
Platform, the Caledonian, Variscan and Carpathian orogenic fronts,
the Tornquist–Teisseyre Zone (TTZ) and the Sorgenfrei–Tornquist
Zone (STZ) (after Pharaoh, 1999, simplified and modified).
been completed in this area (EUGENO-S Working
Group, 1988; BABEL Working Group, 1991; Meissner
et al., 1994), and numerous alternative hypotheses
have been formulated on various aspects of its presentday
crustal structure and geodynamic evolution (e.g.
Pegrum, 1984; Tanner and Meissner, 1996; Berthelsen,
1998). However, even the basic features that
characterise SW Baltic Sea and surrounding areas such
as the extent of Baltica and Avalonia blocks, existence
of the Trans-European Fault, and the presence and
exact location of Caledonian deformation front are still
discussed and no consensus has been reached yet
(Thybo, 1997, 2001; Franke, 1990; Dadlez, 2000;
Lassen et al., 2001; McCann and Krawczyk, 2001).
During Permian through Cretaceous times several
sedimentary basins and sub-basins of the so-called
Peri-Tethys domain developed in Western and Central
Europe due to post-orogenic destruction of the Variscan
foreland initiated by Late Carboniferous wrenching
and strike-slip movements (Brochwicz-Lewiński
et al., 1984; Ziegler, 1990; van Wees et al., 2000).
Significant subsidence and deposition took place
along the Sorgenfrei–Tornquist Zone in Scania and